Or you are observing evolution in action. A bioluminescent spider would likely be an easy target for birds or bats. One by the lamp is not because hunters have

Or you are observing evolution in action. A bioluminescent spider would likely be an easy target for birds or bats. One by the lamp is not because hunters have simply not adapted yet. Or maybe, spider webs used to be enormous and profitable everywhere, only that insects dying globally makes them profitable now only in those light spots.